US President George W Bush is in Germany at the start of a week-long tour of Europe aimed at boosting support for his war on terror and narrowing differences with his allies.

We think that Bush is the biggest terrorist of the world... His father was a killer too

Lucy Schnell Protester

His arrival in Berlin was marked by protests by thousands of German demonstrators, and some clashes have been reported.

Speaking after the president's plane touched down, US Secretary of State Colin Powell said Iraq would be on the agenda.

Concern has been voiced by many European politicians since President Bush outlined what he called an "axis of evil" earlier this year comprising Iraq, Iran and North Korea - potential targets of the US-led war on terror.

Mr Powell said the Berlin visit would celebrate the strong relationship between Germany and the United States, although he conceded there were disagreements on trade.

Berlin agenda

In central Berlin, crowds of about 20,000 anti-war demonstrators were kept well away from President Bush and German Chancellor Gerhard Schroeder as they dined near the Brandenburg Gate.

Iraq features on Bush's talks agenda

"We think that Bush is the biggest terrorist of the world... His father was a killer too," said Lucy Schnell who was among the protestors.

However repeated clashes between protesters and police broke out after a march by anti-globalisation demonstrators, left-wing and anarchists groups had begun peacefully.

About 400 demonstrators threw bottles and stones at the police, who responded with baton charges and made several arrests.

Some 10,000 police officers were mobilised to try to prevent any violence, in one of the biggest security operations in the city's history.

The BBC's Rob Broomby, at the protests, said the atmosphere was troubled and tense.

Mr Bush is to speak to the German parliament in the historic Reichstag building on Thursday.

Arms treaty

The centrepiece of the Bush tour will be the signing of a new arms treaty with Russia, slashing nuclear arsenals by two-thirds.

Mr Bush will travel to Moscow on Thursday afternoon.

Bush tour

Wednesday - arrive Germany Thursday - address German parliament, fly to Moscow Friday - meet Putin, sign arms control treaty Saturday - visit St Petersburg Sunday - fly to Paris, meet Chirac Monday - visit French US war cemetery, travel to Rome, meet Pope Tuesday - Nato summit, return home

As Mr Bush set out on his trip, European Commission President Romano Prodi called for Europe to start speaking "with a single voice" in foreign policy matters if it wanted to be taken seriously by America.

He told the European Parliament that trade was the only area in foreign policy "where the EU is on an equal footing with the United States".

Mr Prodi also called for a single European police force to fight terrorism and organised crime.

The US drive to expand the war on terror has met with some resistance in Europe.

Speaking to reporters before Air Force One departed for Berlin, Mr Bush said: "Our alliance must remain tough in the war against global terror."

Mr Bush will also be seeking to close gaps over a number of other issues, including the death penalty, the creation of an international criminal court, trade tariffs and policy towards the Middle East.

"Even though we've had some initial successes, there's still danger for countries which embrace freedom, countries such as ours, or Germany, France, Russia, or Italy," said Mr Bush.

His six-day trip will culminate in a Nato summit in Italy.